The present invention is related to a storage control unit which is connected between a host unit, and a storage unit such as an external RAID unit, and controls data transfer between the host unit and the RAID or other external storage unit. In particular, the present invention is related to a storage system which has a distinctive structure for connecting the storage control unit and the external storage unit.
The host unit can include a plurality of host computers or a single host computer with a plurality of ports, and the external storage unit includes a plurality of individual storage units, for example, such as hard disk drives.
With the increasing scale of computer storage systems, faster data processing, and increasing amounts of data, it is necessary for a storage control unit to have improved performance, reliability and availability. Typically, to improve reliability in a storage control unit, redundant components and connections are used. For example, a plurality of controllers or a plurality of ports is provided.
FIGS. 2 and 3 are examples of connections between a storage control unit and a storage unit. As shown in those figures, the storage control unit has a plurality of control units in communication with dual port structures, and is arranged such that two SCSI access paths from each control unit are connected to the storage units. In the figures, SCSI is an abbreviation of Small Computer System Interface and means an input/output interface comprising SCSI-1 and SCSI-2 where SCSI-1 and SCSI-2 have the same well known specifications, but SCSI-2 also takes into consideration a system in which SCSI-1 units and SCSI-2 units are both used. When it is unnecessary to distinguish SCSI-1 and SCSI-2, SCSI-1 or just SCSI, is used as a general term.
Another way of improving performance and availability is to use optical fiber channel technology to replace SCSI-1. For example, a technology which uses an optical fiber channel to connect a storage control unit to storage units is disclosed in Japanese patent publication 5-241984. As known from the prior art, all these technologies use an optical fiber channel to connect a storage control unit and a host computer. As such, no description of this type of connection is necessary here. Moreover, equipment in which a storage control unit is connected to a storage unit through an optical fiber channel has been introduced as a product. See the disk array system FC5000 made by Data General Corporation.
The conventional means of providing dual access paths between a control unit and storage units is to employ a storage unit which has a plurality of input/output ports (e.g., a dual port magnetic disk device, a dual port magnetic disk unit or other multi-port storage units) so that two access paths are provided in one control unit. When either path fails, the other path is used as the access path.
In a conventional connection structure between a storage control unit and multiple storage units, when trouble occurs on one path (for example, when SCSI-1 port 1-1 breaks down in FIG. 2), access to the storage units connected to the failed path can be executed only through one path from SCSI-1 port 1-2; therefore, concurrent access from the control unit 1 to multiple storage units connected to the failed path through a dual path route is impossible. This means that a function using two data paths generally cannot be used in a mode in which a data transfer operation has priority and in which the dual paths are not continually provided.
In FIG. 3, when SCSI-1 port 1-1 fails, control unit 1 cannot access all the disk units connected to SCSI-1 port 1-1. As a result, access to a target disk unit is executed by control unit 2 which must process it through other communication means.
Similarly, if both paths break down (for example, when SCSI-1 port 1-1 and SCSI-1 port 1-2 break down in FIG. 2), the control unit 1 cannot access all the storage units connected to SCSI-1 port 1-1 and SCSI-1 port 1-2. As a result, access to a target disk unit is executed by control unit 2 which must process it through other communication means (not shown). Thus, when a path breaks down, access to a target disk cannot be executed, communication processing between control units is required, and performance deteriorates.
Further, if the dual access paths are made merely by providing two ports for connecting storage units using fiber channel control chips, etc., manufacturing cost increases. On the other hand, if a system uses one access path, a data transfer operation between the control unit and a plurality of storage units connected to this path that executes primarily by accessing two paths at the same time, cannot be performed and system performance deteriorates.
One objective of the present invention is to provide a system structure where, in normal operation, distinctively constructed dual paths are used as data transfer paths to enable faster access and, when a path failure occurs, to allow continued access to data. The benefit of a dual path structure is provided and manufacturing cost is decreased.
The present invention provides a system structure for a storage control unit having a plurality of control units, where even if a failure occurs on a path between the control unit and the storage units, the control unit itself can still access the target storage unit, minimizing the need to request another control unit to execute the processing. Another benefit of the present invention is that it provides a system structure in which access to a storage unit is processed with distributed access load in the control unit. According to the present invention, these objectives are accomplished by providing a storage control unit that has at least two control units, each of which has a plurality of connecting ports for connecting a plurality of storage units to the control units that manage them. Moreover, a storage control unit is connected to an external storage unit, by a connecting structure in which a connecting port in a first control unit is connected by an access path (transfer path) to a connecting port in a second control unit, and a second connecting port in the first control unit is connected by another access path to a second connecting port in said second control unit. The two paths are connected to a storage unit, and a plurality of such storage units are used. The storage unit includes a magnetic disk unit having a dual port input/output function.
Furthermore, in the structure described above, the present invention provides a connecting structure in which a plurality of storage units connected to the two paths are specified as one group, and striping for a RAID structure is executed in this group. Although RAID means Redundant Array of Independent Disks, it does not necessarily mean a Redundant Array comprising independent disks. RAID systems refers to an external storage system which has a disk array structure of RAID.
A first embodiment of the above-described structure is shown in FIG. 1, in which each storage unit is connected to two parallel, vertical fiber channel loops, each row is a communicating group, and the plurality of groups are vertically arranged. The present invention provides a storage control unit that has at least two control units, each having a plurality of connecting ports for connecting a plurality of storage units to the control units managing these storage units, and each having a connecting structure between a storage control unit and an external storage unit, such that the first connecting port in the first control unit is connected by a fiber channel loop to the first connecting port in a second control unit, a second connecting port in the first control unit is connected by a second fiber channel loop to a second connecting port in the second control unit, the two fiber channel loops are connected to the first storage unit, and a plurality of such storage units is used.
A second embodiment of the present invention provides a storage control unit which has at least two control units, each having a plurality of connecting ports for connecting a plurality of storage units to the control units managing these storage units, and each having a connecting structure between a storage control unit and an external storage unit, such that the first connecting port in the first control unit is connected by a SCSI-1 path to the first connecting port in a second control unit, a second connecting port in the first control unit is connected by a second SCSI-1 path to a second connecting port in said second control unit, the two SCSI-1 paths are connected to the first storage unit, and a plurality of such storage units is used.
Furthermore, in the first embodiment, the present invention provides a connecting structure in which a plurality of storage units connected to the two fiber channel loops are specified as one group, and striping for a RAID structure is executed in this group. In the second embodiment, the present invention provides a connecting structure in which a plurality of storage units connected to said two SCSI-1 paths are specified as one group, and striping for a RAID structure is executed in this group.